This invention generally relates to voltage controlled oscillators, and more specifically, to reducing noise in such oscillators.
In general, a VCO (voltage controlled oscillator) is an oscillator circuit that outputs an AC signal having a frequency that varies in response to an input control voltage. VCOs are fundamental components that are employed in a broad range of applications including radar and communications systems (e.g., wireline or wireless applications) for data transfer and recovery processes. By way of example, VCOs are utilized for PLL (phase locked loop) circuits, DLL (delay locked loop) circuits, and injection locked oscillators. VCOs are further employed for applications such as frequency translation, data modulation, clock distribution and clock/data recovery.
In the operation of a VCO, an undesired random phase component, referred to as phase noise, is often introduced into the oscillator output. This phase noise, which varies over time, may be due to the thermal noise present in the components of the oscillator, loss in the passive components, and to other factors. Oscillator phase noise is a key performance metric in many oscillator applications including many wireless and wireline communications applications, radars, sensors, images, data converters, and so forth.